Right then. If you are going to ask anyone for help with your computer it really helps them if they can eliminate a lot of stuff knowing you have completed each of the steps below. I'll still help you if you don't but it sure helps me a lot if you complete them all first. Oh yeah, and I mostly know Windows so if you've got a Linux or Mac question you might try someone else.

1. What version of Windows am I running?
   IMPORTANT - If you're running anything older than Windows XP it's time to upgrade. This will usually necessitate upgrading your machine as well but what the heck, these days you can get three times what I have for a third of the price that I had to pay when I got my computer. That's the cool thing about computers, the price keeps dropping. Just make sure you are running at least Windows XP as older versions or Windows are no longer supported. If not, go buy a new computer with Windows 7. Click the above link for help figuring out what version of Windows you are running.
2. Firewall
   Simply put, you need one. It's automatic if you have Windows 7 or Windows Vista and if you are running Windows XP, you can enable the one that is included in the Operating System assuming you have the latest Service Pack installed. If you don't have 7 or Vista or XP it's time to upgrade. If you want something a little more advanced than the Windows firewall you might want to get the free version of ZoneAlarm (which you can grab from the above link) and take the time to learn how to set it up and configure it. Don't worry, the default settings are fine for most people. One good thing about ZoneAlarm is that it checks not only incoming traffic but outgoing as well.
3. Microsoft Update
   As of version 6 of Windows Update, Microsoft has combined updates for Windows and Office. You can now go to one site for both and Microsoft is planning on adding more programs in the future. If you are using Windows 2000 or XP, go to this link, install this new version of the Update engine and then click the link to upgrade to Microsoft Update. Then run it. And keep running it until you have installed ALL the Critical Updates. You might want to look through the Recommended Updates if they pertain to you and the Driver Updates if something is not working right. If you have Windows 7 or Vista, simply run Windows Update and then click "Get updates for more products".
4. If you have Windows XP, you can - and should - configure your computer to automatically update itself. Here's how:
   • Open Control Panel | System | Automatic Updates
   • Make sure that this is turned on and under Settings, make sure that the bottom option 'Automatically download...' is selected.
   • Click Apply | OK
5. If you are still running Windows 98, you'll need to get your updates from Windows Update and Office Update. Keep running Windows Update until all the Critical Updates are installed and Office Update until EVERY update is installed. NOTE - You will probably need your original Office CD.
6. AntiVirus
   You have to have it. If you already have anti-virus software installed:
   • Make sure your subscription is current. Most computers come with this pre-installed and it's easy to let it expire after the 30-day 'free trial' period. Having out-of-date virus signature files is worse than not having any anti-virus software at all because you feel safe when you really aren't. So, renew your subscription (if you like what you have) or use free software (what I do).
   • Make sure that the virus signature files are up-to-date by running the 'Update' function until it can't find any more virus signatures; and then configure your software to auto-update itself without any user intervention on a DAILY basis.
   • Then do a complete scan of all your hard drives. Then schedule this scan of all your drives so it happens on a weekly basis. And make sure you are scanning ALL files and are scanning within archives/compressed files.
7. Spyware
   Whew...! Finally you can proceed. Psych... But wait, there's more! Think your computer has not been compromised? Think again. Spyware, data miners and other aggressive advertising and tracking components are undoubtedly running on your computer. You may have installed these programs unknowingly when you installed that last item of shareware or it came bundled legitimately with that media player you just got and you just didn't read the EULA.
8. Now, sign up for the 'Microsoft Security Update for Home Users' here.
   • If you are somewhat technically minded, you should get the Microsoft Security Notification Service instead. This service will send you an email when new patches for vulnerabilities come out for Microsoft products. To subscribe to the Microsoft Security Notification Service, visit http://www.microsoft.com/technet/security/bulletin/notify.mspx.
   • And, if you are using Microsoft Office, you should also sign up for the Office Newsletter which will notify you when there is a new patch available for a product in the Office suite. You can do that at http://office.microsoft.com/en-us/help/ha101864261033.aspx.
   • NOTE - You'll need a Windows Live ID to receive these two notifications which you can get at the same URL where you sign up.
9. Make sure you update all your 3rd party applications/programs. Stuff like most AntiVirus programs, Adobe Reader, Java, Firefox, QuickTime, iTunes and RealPlayer all have nifty update functions built right in. But you need to use them. Running ANY program that is not fully patched is not a good idea. Get the latest version of everything that you use!
10. Lastly, give me a shout and let me know what's wrong with your computer.

Microsoft has boiled all this down to just four steps. You can also double check with them to see if you have done everything that they recommend here.

Ever get an email that purports to have some Microsoft patch attached? DON'T OPEN IT! Microsoft never distributes patches via email, only via sites like Microsoft Update, Windows Update, Office Update, etc. For proof, see Microsoft's Policy on Software Distribution.

Got some time on your hands? Here is Microsoft's Best Security Practices for home users and here are some Microsoft security basics that boil it all down for you.

And don't complain, no one said you had to play. If you do, here are Five Internet Truths to remember.

Lastly, here are some recommended best practices for Windows users. This is an ongoing project and not nearly complete but it might help.